There have been conventionally known a variety of adhesive compositions for being applied to the thread contact face of a screw, bolt, nut or the like for the purpose of locking and sealing up such screw members engaged with each other. As to the conventional adhesive compositions, slurry-like liquefied or paste-like adhesive compositions made by dispersing micro-capsules enclosing a reactive adhesive and a resin serving as a binder in an organic solvent or water are disclosed in Japanese Pat. Publication SHO 45-11051(B), Japanese Pat. Publication SHO 54-1737(B), Japanese Pat. Publication SHO 52-46339(B), Japanese Pat. Appln. Public Disclosure SHO 1-27684(A), and Japanese Pat. Appln. Public Disclosure SHO 1-128918(A).
These adhesive compositions are aimed at strengthening the mutual adhesive force of the screw members by destroying the micro-capsules when engaging the screw members to permit the adhesive to flow out of tile micro-capsules.
However, these adhesive compositions with which the thread contact faces of the screw members are coated are required to be dried. Thus, if the adhesive composition contains an organic solvent, it entails a sanitary problem of generating the gas of the organic solvent in a drying process.
Furthermore, in the case of using the composition containing water, the drying process which is carried out at an ordinary temperature takes much time, and therefore, requires heating treatment, thereby leading to a problem of losing the stability in preservation of the reactive adhesive contained in the micro-capsules.
On the other hand, Japanese Patent Publication HEI 3-8393 discloses an adhesive composition with the object of carrying out the drying process at room temperature for a short time, which composition is made by adding, to a binder such as a monomer or oligomer of a photo-hardening resin which hardens by the action of radiation of ultra-violet rays or the like, micro-capsules containing an opaque filler, a photo-initiator which starts polymerization of the monomer or oligomer when exposing the monomer or oligomer to the radiation, and the polymer thus obtained or its free-radical polymerization initiator which starts polymerization of the oligomer and/or its activator.
Since this adhesive composition has the opaque filler contained in the binder composed of the photo-hardening resin, the radiation such as ultraviolet rays does not reach deep inside the binder, and therefore, only the surface part of the binder which is exposed with the ultraviolet rays is polymerized by the photo-initiator. In this state, only the surface part of the adhesive composition is hardened in the form of a film with the inside part kept in its paste state containing the micro-capsules.
That is to say, the adhesive applied to the thread contact face has its inside part kept in its paste state covered with a film layer. Therefore, the tightening resistance generated when thrusting a screw member into its counterpart at the outset lessens. By further screwing up, the micro-capsules are broken to cause the polymerization initiator or its activator to flow out of the micro-capsules so as to subject the polymer, oligomer, and monomer to polymerization reaction with the polymerization initiator or its activator. Consequently, the effects of sticking and sealing up the screw members are heightened.
However, if the thread contact face of the screw member is left coated with the aforenoted adhesive composition for a long time, a part yet to be hardened of the adhesive composition will be hardened owing to sunlight or heat. This adhesive composition entails a disadvantage such that, even when the polymerization initiator or its activator comes out by tightening up the screw member to break the micro-capsules, no polymerization reaction takes place, and consequently, the effects of sticking and sealing up the screw members cannot be brought about.
In addition, since the aforesaid film contains an inorganic filler, it is disadvantageously fragile, so that a paste-like part yet to be hardened of the adhesive composition may come out when carrying the screw member such as a bolt in the stage of distribution.